Creating event creates a duplicate task

[John Fossey]

For some reason, whenever I create an Event in my Lightning calendars, it also creates a duplicate Task, which appears in the calendar but not in the list of Tasks. Then when I try to delete the extra Task created it says Error 404 - Task not found, and won't delete.

I'm using TB 11.0 with Lightning 1.3, and using memotoo.com for synchronizing calendars& tasks between two computers. The duplicate Tasks don't appear in memotoo, however.

Any ideas how to correct this?